The Yavaros lagoon system in Sonora Mexico and the Huizache-Caimanero lagoon system in Sinaloa Mexico (Fig.l) are areas of considerable economic importance given their high shrimp production. They are located in zones with different climate, drainage characteristics, agricultural activity, soil composition and movement of particulates, parameters which have been reported by Livingstone (1978) to be important factors in the accumulation of organochlorine residues. In order to study the distribution and concentration of organochlorine compounds in these lagoons, they were measured in organisms (Rosales 1983) and sediments of the two areas. The Yavaros complex consists of the Yavaros, Moroncarit and Etchoropo Lagoons. Each of these lagoons receives drainage water from an extensive agricultural area based on the River Mayo waters. The climate of this area i~ semi-arid with low rainfall. The Huizache-Caima nero system consists of a large two-basined lagoon located between the Baluarte River in the southeast and the Presidio River in the northwest. The lagqons are communicated with the rivers through two narrow channels i0 km long. The Huizache-Caimanero area has a tropical climate with high summer rainfall (Ortega 1976). In the present study the analysis of the concentration of organochlorine compounds in sediments of the two lagoon systems during a period of 21 months allows us to suggest the relative importance of the different factors that affect the accumulation of these compounds. 1 Contribution No. 356 of the Instituto de Ciencias del Mar y Limnonog~a, UNAM.